Network Modeling Reveals Cross Talk of MAP Kinases during Adaptation to Caspofungin Stress in Aspergillus fumigatus

Abstract

Mitogen activated protein kinases (MAPKs) are highly conserved in eukaryotic organisms. In pathogenic fungi, their activities were assigned to different physiological functions including drug adaptation and resistance. Aspergillus fumigatus is a human pathogenic fungus, which causes life-threatening invasive infections. Therapeutic options against invasive mycoses are still limited. One of the clinically used drugs is caspofungin, which specifically targets the fungal cell wall biosynthesis. A systems biology approach, based on comprehensive transcriptome data sets and mathematical modeling, was employed to infer a regulatory network and identify key interactions during adaptation to caspofungin stress in A. fumigatus. Mathematical modeling and experimental validations confirmed an intimate cross talk occurring between the cell wall-integrity and the high osmolarity-glycerol signaling pathways. Specifically, increased concentrations of caspofungin promoted activation of these signalings. Moreover, caspofungin affected the intracellular transport, which caused an additional osmotic stress that is independent of glucan inhibition. High concentrations of caspofungin reduced this osmotic stress, and thus decreased its toxic activity. Our results demonstrated that MAPK signaling pathways play a key role during caspofungin adaptation and are contributing to the paradoxical effect exerted by this drug.

Genome-wide transcriptome analysis ofAspergillus fumigatusexposed to osmotic stress reveals regulators of osmotic and cell wall stresses that are SakAHOG1and MpkC dependent

“…Both Δ atfA Afs35 and Δ atfA CEA17 had decreased growth in 1.2 M sorbitol (Figure a), while Δ atfB‐D CEA17 showed comparable growth with the wild‐type strain (data not shown). Alterations in osmolarity can have an impact on the composition and structure of the cell wall (Valiante et al, ; Altwasser et al, ; Winkelströter et al, a; Bom et al, ; Bruder Nascimento et al, ). In accordance, both Δ atfA Afs35 and Δ atfA CEA17 mutants were sensitive to the cell wall‐damaging agents calcofluor white and Congo red.…”

“…Another interesting aspect was the upregulation upon osmotic stress of several genes encoding for protein kinases related to calcium and TOR, such as calcium calmodulin (CmkD showed only a discrete increase. It has been proposed that increased concentrations of caspofungin promoted activation and cross-talk between the A. fumigatus MpkA and SakA pathways (Altwasser et al, 2015;Bruder Nascimento et al, 2016;Valiante et al, 2015b). Additionally, the existence of a salvage pathway, possibly dependent on MpkC and SakA, which would compensate the caspofungin stress response, has been proposed (Valiante et al, 2015b).…”

“…The MpkC protein sequence is very similar to that of SakA (68.4% identity; 82.9% similarity; BLAST e-value: 2e-147). SakA and MpkC have also been shown to play a role in caspofungin adaptation and carbon source utilization, respectively (Reyes, Romans, Nguyen, & May, 2006;Altwasser et al, 2015;Valiante, Macheleidt, Föge, & Brakhage, 2015a).…”

The Aspergillus fumigatus SchASCH9 kinase modulates SakAHOG1 MAP kinase activity and it is essential for virulence

“…In A. fumigatus MpkC and SakA are paralogues of the S. cerevisiae Hog1, which is the main regulator of the HOG pathway (Maeda et al, 1994). SakA and MpkC play a role in carbon utilization and adaptations to the antifungal agent, caspofungin (Reyes et al, 2006;Altwasser et al, 2015;Valiante et al, 2015). Pascual-Ahuir and Proft (2007) have shown that Sch9 is involved in the regulation of adaptations to acute hyperosmotic stress in S. cerevisiae.…”

Gene Regulatory Cross Networks: Inferring Gene Level Cell-to-Cell Communications of Immune Cells

“…GCCN is similar to the widely used term cross-talk network but we make the distinction between the two as the following: GCCN only refers to gene level communications, whereas cross-talk network term is used to describe communication in any molecular levels between different cell-types. In summary, the defined GRCN and GCCN terms of this study are more specific than the well-established crosstalk networks (CTN) term that is widely used for any type of network that refers to communication between different cell types at any molecular level [10][11][12][13][14][15]. We consider that GRCN and GCCN are yet to be explored as a relatively new avenue of research and catch up with the classical gene networks inference research of single cell types.…”